The present invention relates to the communications arts. It finds particular application in conjunction with improving intelligibility in noisy environments on both a near-end and a far-end of a network and it will be described with particular reference thereto. However, it is to be understood that the invention may find further application outside of the network environment, such as in telecommunications components themselves, or in individual gateways or portals to a telecommunications network.
Many present day communication systems provide unpleasant speech quality in the presence of background noise on both a transmit or far-end, and on a receive or near-end. Additional complexity is introduced by the varied sources of noise ranging from noisy background environments to acoustic and/or electrical echoes. With respect to background noise, the problem potentially exists on both the near-end and the far-end of the communications network. For example, consider a cellular telephone user making a call from a busy street corner. Typical communication systems are not able to adequately distinguish background noise from voice information, with the result that the system attempts to transmit both voice and noise over the communications link. At the other end of the link, this transmitted noise degrades the quality of the received voice signal. Compounding the problem, many such devices incorporate speech coders so as to reduce the bit rate that must be transmitted over the communications channel. Although bit rate reduction is desirable in that it permits the capacity of the wireless communication system to be increased, it renders the communication system increasingly vulnerable to speech quality degradations in the presence of background noise.
Background noise at the receiving end or near-end of the network can also impair intelligibility of the voice signal. For example, consider a telephone call placed to a factory office. High levels of ambient factory noise can degrade the intelligibility of the voice signal received, sometimes requiring the caller to repeat information.
Other known sources of undesirable noise include acoustic echo caused by, for example, a transmitter both receiving a voice signal directly and through echo paths. While prior art echo controllers exist, they typically function by detecting the echo and canceling the signal. However, typical telecommunications users are uncomfortable with periods of total silence interspersed within a voice call. Some systems introduce a white noise signal instead of the silence generated upon echo detection which undesirably only match the noise power but not the spectrum. In other words, the white noise sounds different, or has different spectral characteristics, than the ambient noise.
The present invention contemplates a new and improved method and apparatus to improve intelligibility of a speech signal transmitted over a communications network which overcomes the above referenced problems and others.
In accordance with one aspect of the present invention, a method of processing a signal between a near-end and a far-end of a telephone network includes receiving both a near-end signal and a far-end signal. A near-end noise component is estimated from the near-end signal, while a far-end noise component is estimated from the far-end signal. Based on the near-end noise component and the far-end noise component, the far-end signal is adjusted to generate a modified signal.
In accordance with another aspect of the present invention, the far-end signal is adjusted by steps including determining a gain as a function of the estimated far-end noise component, and applying the gain to the far-end signal.
In accordance with another aspect of the present invention, the determining a gain step includes determining a first gain derived from the estimated far-end noise component and a second gain derived from the near-end signal and the far-end signal. The first and second gains are then combined and thresholded.
In accordance with another aspect of the present invention, the first gain is determined by comparing a set of critical frequency bands and the estimated far-end noise component.
In accordance with another aspect of the present invention, the second gain is determined by applying a near-end gain compensation to the determining of the second gain.
In accordance with another aspect of the present invention, the far-end signal is adjusted by selectively mixing a thresholded estimated far-end noise component into the far-end signal.
In accordance with another aspect of the present invention, the far-end noise component is estimated by splitting the far-end signal into a uniform set of frequency bands and converting those bands to a set of critical frequency bands selected for characteristics including the human auditory system. Samples of the set of critical frequency bands are then prefiltered to discard a sample minima shorter than a specified minimum. The plurality of independent filterings are performed to provide an estimate of a smallest sample in a sample set where the estimated far-end noise component includes the estimate of the smallest sample.
In accordance with another embodiment of the present invention, a method of processing a signal to enhance intelligibility in noisy environments includes in the frequency domain estimating a noise component of the signal and calculating a first gain based on the estimated noise component. Still in the frequency domain, a second gain is determined as a function of the far-end echo. The signal is then adjusted as a function of the first and second gain producing a modified signal.
In accordance with another aspect of the present invention, the method further includes in the time domain, adjusting the modified signal as a function of signal level, dynamic range, and identification of the signal as either speech or noise. A gain is applied to compensate for a noise component estimated on the near-end signal.
In accordance with another aspect of the present invention, the method further includes in the frequency domain, combining the first and the second gain, resulting in a master gain, and then thresholding that gain.
In accordance with another aspect of the present invention, the method further includes in the frequency domain estimating a noise component of the near-end signal, and in the time domain, applying a third gain to the signal, where the third gain is a function of the estimated near-end noise.
In accordance with another embodiment of the present invention, an apparatus for enhancing intelligibility of a far-end signal in noisy environments includes a first noise estimator which estimates a far-end noise component from the far-end signal. A first calculator then determines a first gain as a function of the estimated far-end noise component. A gain filter applies the calculated first gain to the far-end signal, and an automatic level controller adjusts the far-end signal as a function of signal level, dynamic range of the system, and identification of the signal as speech or noise.
In accordance with another aspect of the present invention, the apparatus further includes a second noise estimator which estimates a near-end noise component in a near-end signal. A noise compensator then applies a second gain to the far-end signal responsive to the estimated near-end noise component.
In accordance with another aspect of the present invention, the first calculator includes a noise reduction gain calculator which calculates a noise reduction gain to reduce far-end noise in the signal. An echo gain calculator calculates an echo control gain to reduce echos detected in the apparatus. A master gain calculator is also provided which combines the echo control gain and the noise control gain into a master gain.
In accordance with another aspect of the present invention, the first calculator also includes a thresholder to confine the master gain to a selected limit.
One advantage of the present invention resides in improved intelligibility in noisy environments provided by both noise reduction and noise compensation. Noise reduction addresses the noise in the signal itself by spectrally attenuating its components. Noise compensation, on the other hand, addresses the acoustic background noise that a person is exposed to while listening to another person on the phone.
Yet another advantage of the present invention resides in the determination of echo based on at least one processed signal by compensating the processing gain.
Further scope of the applicability of the present invention will become apparent from the detailed description provided below. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those of skill in the art.